The Study: We know prophylactic tamoxifen can reduce breast cancer events in high-risk women, but it also comes with lots of side effects. But does one dose have to fit all? Now that’s a surprisingly novel question. In the TAM-01 trial, women with resected intra-epithelial neoplasia were randomized to 3 years of daily placebo or reduced-dose tamoxifen at 5 mg instead of 20 mg. Those with DCIS that was high grade or had comedo necrosis (45%) also received adjuvant radiation, but there were really no major exclusion criteria. This resulted in a pretty heterogeneous population including roughly 45% with grade 1 or 2 DCIS, 25% with grade 3 DCIS, 20% with ADH, and 10% with LCIS. “Whoa,” you say, “full dose endocrine therapy is kinda standard in some of those folks, right?” Right, but wait for it. Reduced-dose tamoxifen produced a significant 40-50% relative reduction (11→ 6.4%) in overall breast cancer events, including a 75% relative reduction in contralateral invasive breast cancer. In addition, there was only a slight increase in hot flashes and no increase whatsoever in the risk of endometrial cancer or embolic event.
Bottom Line: Lower doses and shorter durations of tamoxifen are still effective at preventing breast cancer. | DeCensi, J Clin Oncol 2019